Applications may run in multiple servers in a cloud service and may requires access to a storage system external to the cloud service. Whenever the applications read, write, or delete content, the external storage system itself enforces quotas, such as the storage space available to the applications. This quota enforcement is provided at the server side and, therefore, the applications are unaware of the current status of the storage or the available space. This makes it difficult to scale out applications on the cloud service when the available storage in a remote system cannot be tracked by the cloud service. Specific interfaces to the external storage or knowledge of the external storage's operation is required to allow the cloud service to track available storage and to keep cloud applications within quotas.
Problems arise when cloud service tenants want to use existing external storage systems that do not provide functionality required by the cloud service for tracking quotas. For example, the external storage systems may provide limited quota enforcement, such as only at the root level and not per folder or per tenant.